In vitro photodynamic inactivation (PDI) of pathogenic germs inducing onychomycosis

Onychomycosis is a fungal nail infection caused primarily by the dermatophytes Trichophyton rubrum and Trichophyton interdigitale or, less frequently, by molds like Aspergillus spp. and Scopulariopsis brevicaulis. Photodynamic treatment of onychomycosis is considered a promising future therapy to overcome the frequent failure of currently used antifungals. In this study, we tested the potential of three photosensitizers for photodynamic inactivation of the onychomycosis causing pathogens T. rubrum, T. interdigitale and S. brevicaulis. Photosensitizers used are 10,15,20-Tetrakis(1-methylpyridinium-4-yl) porphyrintetra(p-toluenesulfonate) (TMPyP), 5,10,15-tris-(1-methylpyridinium-2-yl)corrolato-(trans-dihydroxo)phosphorus(V) (PCor⁺) and 2',4',5',7'-tetrabromo-3',6'-dihydroxyspiro[2-benzofuran-3,9'-xanthene]-1-one (Eosin Y). The phototoxic effects caused by the cationic photosensitizers (PCor⁺ and TMPyP) were tested on suspension cultures of spores as well as on fungi during growth on surfaces where both photosensitizers cause high phototoxicity. The anionic Eosin Y was tested on surface-growing fungi only and induces remarkable phototoxic effects on dermatophytes and molds. In all cases, no spore regrowth was detected after PDI. This study is considered a first step towards successful and cost efficient treatment of onychomycosis.